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Computability and recursion
 BULL. SYMBOLIC LOGIC
, 1996
"... We consider the informal concept of “computability” or “effective calculability” and two of the formalisms commonly used to define it, “(Turing) computability” and “(general) recursiveness.” We consider their origin, exact technical definition, concepts, history, general English meanings, how they b ..."
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We consider the informal concept of “computability” or “effective calculability” and two of the formalisms commonly used to define it, “(Turing) computability” and “(general) recursiveness.” We consider their origin, exact technical definition, concepts, history, general English meanings, how they became fixed in their present roles, how they were first and are now used, their impact on nonspecialists, how their use will affect the future content of the subject of computability theory, and its connection to other related areas. After a careful historical and conceptual analysis of computability and recursion we make several recommendations in section §7 about preserving the intensional differences between the concepts of “computability” and “recursion.” Specifically we recommend that: the term “recursive ” should no longer carry the additional meaning of “computable” or “decidable;” functions defined using Turing machines, register machines, or their variants should be called “computable” rather than “recursive;” we should distinguish the intensional difference between Church’s Thesis and Turing’s Thesis, and use the latter particularly in dealing with mechanistic questions; the name of the subject should be “Computability Theory” or simply Computability rather than
Physical Hypercomputation and the Church–Turing Thesis
, 2003
"... We describe a possible physical device that computes a function that cannot be computed by a Turing machine. The device is physical in the sense that it is compatible with General Relativity. We discuss some objections, focusing on those which deny that the device is either a computer or computes a ..."
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Cited by 13 (0 self)
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We describe a possible physical device that computes a function that cannot be computed by a Turing machine. The device is physical in the sense that it is compatible with General Relativity. We discuss some objections, focusing on those which deny that the device is either a computer or computes a function that is not Turing computable. Finally, we argue that the existence of the device does not refute the Church–Turing thesis, but nevertheless may be a counterexample to Gandy’s thesis.
The history and concept of computability
 in Handbook of Computability Theory
, 1999
"... We consider the informal concept of a “computable ” or “effectively calculable” function on natural numbers and two of the formalisms used to define it, computability” and “(general) recursiveness. ” We consider their origin, exact technical definition, concepts, history, how they became fixed in th ..."
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Cited by 5 (1 self)
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We consider the informal concept of a “computable ” or “effectively calculable” function on natural numbers and two of the formalisms used to define it, computability” and “(general) recursiveness. ” We consider their origin, exact technical definition, concepts, history, how they became fixed in their present roles, and how
Computability and Incomputability
"... The conventional wisdom presented in most computability books and historical papers is that there were several researchers in the early 1930’s working on various precise definitions and demonstrations of a function specified by a finite procedure and that they should all share approximately equal cr ..."
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The conventional wisdom presented in most computability books and historical papers is that there were several researchers in the early 1930’s working on various precise definitions and demonstrations of a function specified by a finite procedure and that they should all share approximately equal credit. This is incorrect. It was Turing alone who achieved the characterization, in the opinion of Gödel. We also explore Turing’s oracle machine and its analogous properties in analysis. Keywords: Turing amachine, computability, ChurchTuring Thesis, Kurt Gödel, Alan Turing, Turing omachine, computable approximations,
Algorithmic Social Sciences Research Unit
, 2012
"... Bourbaki’s destructive � influence on the mathematization of economics � K. Vela Velupillai ..."
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Bourbaki’s destructive � influence on the mathematization of economics � K. Vela Velupillai
Effective computation by humans and machines
, 2002
"... There is an intensive discussion nowadays about the meaning of effective computability, with implications to the status and provability of the Church–Turing Thesis (CTT). I begin by reviewing what has become the dominant account of the way Turing and Church viewed, in 1936, effective computability. ..."
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There is an intensive discussion nowadays about the meaning of effective computability, with implications to the status and provability of the Church–Turing Thesis (CTT). I begin by reviewing what has become the dominant account of the way Turing and Church viewed, in 1936, effective computability. According to this account, to which I refer as the Gandy–Sieg account, Turing and Church aimed to characterize the functions that can be computed by a human computer. In addition, Turing provided a highly convincing argument for CTT by analyzing the processes carried out by a human computer. I then contend that if the Gandy–Sieg account is correct, then the notion of effective computability has changed after 1936. Today computer scientists view effective computability in terms of finite machine computation. My contention is supported by the current formulations of CTT, which always refer to machine computation, and by the current argumentation for CTT, which is different from the main arguments advanced by Turing and Church. I finally turn to discuss Robin Gandy’s characterization of machine computation. I suggest that there is an ambiguity regarding the types of machines Gandy was postulating. I offer three interpretations, which differ in their scope and limitations, and conclude that none provides the basis for claiming that Gandy characterized finite machine computation.
Post’s Machine.
"... In 1936 Turing gave his answer to the question ”What is a computable number? ” by constructing his now wellknown Turing machines as formalisations of the actions of a human computor. Less wellknown is the almost synchronously published result by Emil Leon Post, in which a quasiidentical mechanism ..."
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In 1936 Turing gave his answer to the question ”What is a computable number? ” by constructing his now wellknown Turing machines as formalisations of the actions of a human computor. Less wellknown is the almost synchronously published result by Emil Leon Post, in which a quasiidentical mechanism was developed for similar purposes. In 1979 these Post ”toy ” machines were described in a little booklet, called ”Post’s machine ” by the Russian mathematician Uspensky. The purpose of this text was to advance abstract concepts as algorithm and programming for school children. In discussing this booklet in relation to the historical text it is based on, the author wants to show how this kind of ideas cannot only help to teach school children some of the basics of computer science, but furthermore contribute to a training in formal thinking. 1
Quantum Computation: A Computer Science Perspective
, 2005
"... The theory of quantum computation is presented in a self contained way from a computer science perspective. The basics of classical computation and quantum mechanics is reviewed. The circuit model of quantum computation is presented aspects of computation and the interplay between them. This report ..."
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The theory of quantum computation is presented in a self contained way from a computer science perspective. The basics of classical computation and quantum mechanics is reviewed. The circuit model of quantum computation is presented aspects of computation and the interplay between them. This report is presented as a Master’s thesis at the department of Computer Science and Engineering at Göteborg University, Göteborg, Sweden. The text is part of a larger work that is planned to include chapters on quantum algorithms, the quantum Turing machine model and abstract approaches to quantum computation.
BOOK REVIEWS CLASSICAL RECURSION THEORY
"... Computational concerns are ancient in mathematical history. If one asks a mathematician to name an algorithm (a word derived from the name of Mohammed alKhowarizimi, ninth century), the immediate response would more often than not be the Euclidean algorithm. The concern with computability has its r ..."
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Computational concerns are ancient in mathematical history. If one asks a mathematician to name an algorithm (a word derived from the name of Mohammed alKhowarizimi, ninth century), the immediate response would more often than not be the Euclidean algorithm. The concern with computability has its reason, as an important part of the power of mathematics lies in the ability to produce numerical answers: to compute, for example, an area, a trajectory, or the expected gain—or loss—on a commercial enterprise. If one seeks an algorithmic solution to a specific problem, no general theory is needed—anything goes; this is the typical—and justified—attitude of mathematical practice. A general theory of algorithms was slow in coming. In fact, the theory emerged only when mathematicians started to doubt whether certain problems were algorithmically solvable. This theory is the product of the first half of our century. There were some earlier attempts. Leibniz dreamt of an algorithmic solution to all problems of reasoning, but had little to offer in terms of a general theory. Charles Babbage and his calculating